Refrigerator

ABSTRACT

A refrigerator is provided in which a refrigerant supplied to an evaporator is precooled to a dryness of nearly zero and is supplied in a single liquid phase to increase the amount of heat exchanged by the evaporator, thereby improving cooling performance or reducing the size of the evaporator. A refrigerator ( 1 ) has a refrigeration cycle ( 8 ) formed by sequentially connecting a compressor ( 2 ) that compresses a refrigerant, a condenser ( 3 ) that condenses the high-pressure gas refrigerant, an economizer ( 4 ) that evaporates some of the condensed liquid refrigerant to cool the liquid refrigerant by means of the latent heat of evaporation thereof and that has a circuit for injecting the evaporated medium-pressure refrigerant into an intermediate inlet of the compressor, an expansion valve ( 5 ) that adiabatically expands the liquid refrigerant, and an evaporator ( 7 ) that evaporates the adiabatically expanded refrigerant, and a refrigerant precooler ( 15 ) that precools the refrigerant supplied to the evaporator ( 7 ) is disposed between the economizer ( 4 ) and the evaporator ( 7 ).

TECHNICAL FIELD

The present invention relates to refrigerators, and particularly to arefrigerator suitable for application to a turbo refrigerator using aplate heat exchanger as an evaporator.

BACKGROUND ART

Turbo refrigerators, conventionally used as high-capacity heat sourcesystems, use shell-and-tube heat exchangers suitable for exchange oflarge amounts of heat as condensers and evaporators. Recently, however,dramatic advances in manufacturing technology have enabled themanufacture of turbo refrigerators with relatively low capacities,namely, less than 100 tons of refrigeration. Such low-capacity turborefrigerators use plate heat exchangers in place of shell-and-tube heatexchangers. On the other hand, turbo refrigerators have high-efficiencyperformance characteristics and accordingly require the plate heatexchangers that are used to have large-size, high-performancespecifications.

A typical plate heat exchanger has a structure in which a plurality ofplates are stacked in parallel such that a plurality of refrigerantchannels and a plurality of cooled-medium channels are alternatelyarranged therebetween; therefore, a major challenge that is faced whenused as an evaporator is how to evenly distribute a refrigerant in avapor-liquid two-phase state among the plurality of refrigerant channelsat the entrance of the evaporator. Specifically, because thevapor-liquid two-phase refrigerant contains a large volume ofvapor-phase refrigerant, an unbalanced flow due to the difference inpressure loss between the individual channels causes the liquid-phaserefrigerant to be distributed in an unbalanced manner among theplurality of refrigerant channels and therefore results in an unevendistribution of the liquid-phase refrigerant, thus posing a problem inthat its heat exchange performance (cooling performance) is decreasedbecause of ineffective utilization of the heat transfer area.

Patent Document 1 proposes a refrigerator in which a nozzle and orificesare provided at a refrigerant entrance of a plate heat exchanger toevenly distribute a refrigerant among a plurality of refrigerantchannels by alleviating the difference in pressure loss, thuseffectively utilizing the entire heat transfer surface of the heatexchanger for improved cooling capacity. Also, to prevent a drop inefficiency due to pressure losses at the orifices in the case whereplate heat exchangers are arranged in series as multiple stages toincrease the amount of heat exchanged, Patent Document 2 proposes arefrigerator having an orifice mechanism, namely, through-holes, only atthe front-end plate heat exchanger and a vapor-liquid separator disposedin piping connecting the plurality of plate heat exchangers so that agas refrigerant separated by the vapor-liquid separator is returned tothe downstream side of the back-end plate heat exchanger.

Patent Document 1:

Japanese Unexamined Patent Application, Publication No. 2001-165590

Patent Document 2:

Japanese Unexamined Patent Application, Publication No. 2005-337688

DISCLOSURE OF INVENTION

The refrigerators disclosed in Patent Documents 1 and 2 above, however,are the same in that both include a refrigerant distributor having anorifice mechanism at a refrigerant entrance of a plate heat exchanger toevenly distribute a refrigerant in a vapor-liquid two-phase state amonga plurality of refrigerant channels. Hence, both share a problem in thata drop in efficiency due to a pressure loss at the orifice mechanism isunavoidable and that the plate heat exchanger has a complicatedstructure and is expensive.

In a refrigeration cycle, a refrigerant at an entrance of an evaporatoris normally in a vapor-liquid two-phase state and has a relatively lowdryness, namely, about 0.1. Nevertheless, the vapor-phase refrigerantaccounts for a predominantly large volume and, as described above, makesit difficult to evenly distribute the liquid-phase refrigerant among aplurality of refrigerant channels, thus constituting the underlyingcause of the above problem. Accordingly, to improve the heat exchangeefficiency of an evaporator for size reduction and improved performance,the challenge, which is not limited to the case where a plate heatexchanger is used, lies in how to bring the state of the refrigerant atthe entrance of the evaporator closer to a single liquid phase.

An object of the present invention, which has been made in light of suchcircumstances, is to provide a refrigerator in which a refrigerantsupplied to an evaporator can be precooled to a dryness of nearly zeroand be supplied in a single liquid phase to increase the amount of heatexchanged by the evaporator, thereby improving cooling performance orreducing the size of the evaporator.

To solve the above problem, a refrigerator of the present inventionemploys the following solutions.

That is, a first aspect of a refrigerator according to the presentinvention is a refrigerator having a refrigeration cycle formed bysequentially connecting a compressor that compresses a refrigerant, acondenser that condenses the high-pressure gas refrigerant, aneconomizer that evaporates some of the condensed liquid refrigerant tocool the liquid refrigerant by means of the latent heat of evaporationthereof and that has a circuit for injecting the evaporatedmedium-pressure refrigerant into an intermediate inlet of thecompressor, an expansion valve that adiabatically expands the liquidrefrigerant, and an evaporator that evaporates the adiabaticallyexpanded refrigerant, and a refrigerant precooler that precools therefrigerant supplied to the evaporator is disposed between theeconomizer and the evaporator.

According to the first aspect, the refrigerant precooler disposedbetween the economizer and the evaporator can precool the refrigerantsupplied to the evaporator to a dryness of nearly zero to supply therefrigerant in a liquid phase to the evaporator. As a result, thetemperature of the liquid refrigerant can be decreased at the samepressure to achieve a larger temperature difference between the liquidrefrigerant and a cooled medium cooled by the evaporator. This ensuresimprovement in the refrigeration capacity and COP (coefficient ofperformance) by the economizer effect and allows a larger amount of heatto be exchanged at the same heat transfer coefficient, thus improvingcooling performance or reducing the size of the evaporator.

In the refrigerator of the first aspect, additionally, the refrigerantprecooler may evaporate some of the liquid refrigerant to cool theliquid refrigerant by means of the latent heat of evaporation thereofand may have a circuit for returning the evaporated refrigerant to arefrigerant intake circuit between the evaporator and the compressor.

According to the first aspect, because the refrigerant precooler usessome of the liquid refrigerant circulated through the refrigerationcycle as a heat sink to precool the refrigerant by means of the latentheat of evaporation thereof, it is possible to efficiently precool theliquid refrigerant and also to simplify the structure of the refrigerantprecooler for ease of installation without the need to supply anexternal heat sink.

In the refrigerator of the first aspect, additionally, the refrigerantprecooler may be constituted of a refrigerant-refrigerant heat exchangerthat precools the liquid refrigerant by heat exchange with a refrigerantshunted from the liquid refrigerant and depressurized and that has acircuit for returning the evaporated refrigerant to a refrigerant intakecircuit between the evaporator and the compressor.

In the above structure, because the refrigerant precooler is constitutedof the refrigerant-refrigerant heat exchanger that performsrefrigerant-refrigerant heat exchange and that has the circuit forreturning the evaporated refrigerant to the refrigerant intake circuitbetween the evaporator and the compressor, the refrigerant precoolerused needs no special structure, and an existing refrigerant-refrigerantheat exchanger can be directly applied. Accordingly, the refrigerantprecooler can be provided at low cost.

In the refrigerator having the above structure, additionally, theeconomizer may be constituted of an intermediate cooler that evaporatessome of the condensed liquid refrigerant to cool the liquid refrigerantby means of the latent heat of evaporation thereof, and the refrigerantmay be a mixed refrigerant such as R410A.

In the above structure, because the economizer is constituted of theintermediate cooler that performs refrigerant-refrigerant heat exchangeand the refrigerant precooler is constituted of therefrigerant-refrigerant heat exchanger, the economizer and therefrigerant precooler do not change the composition of the refrigeranteven if the refrigeration cycle uses a mixed refrigerant, such as R410A,whose composition changes as a result of self-expansion. Accordingly,the rated capacity can be delivered without the possibility of unstablecapacity due to changes in the composition of the refrigerant.

In the refrigerator of the first aspect, additionally, the refrigerantprecooler may be constituted of a vapor-liquid separator that separatesthe liquid refrigerant into a liquid-phase refrigerant and a vapor-phaserefrigerant and that has a circuit for returning the vapor-phaserefrigerant having precooled the liquid-phase refrigerant by evaporationand separation to a refrigerant intake circuit between the evaporatorand the compressor.

According to the first aspect, because the refrigerant precooler isconstituted of the vapor-liquid separator that separates the liquidrefrigerant into a liquid-phase refrigerant and a vapor-phaserefrigerant and that has the circuit for returning the vapor-phaserefrigerant having precooled the liquid-phase refrigerant by evaporationand separation to the refrigerant intake circuit between the evaporatorand the compressor, the refrigerant precooler used needs no specialstructure, and an existing vapor-liquid separator can be directlyemployed. Accordingly, the refrigerant precooler can be provided at lowcost.

In the refrigerator of the first aspect, additionally, the evaporatormay be constituted of a plate heat exchanger including a plurality ofplates stacked in parallel such that a plurality of refrigerant channelsand a plurality of cooled-medium channels are alternately arranged.

In the above structure, because the refrigerant can be precooled to adryness of nearly zero and be supplied to the evaporator in a liquidphase, even if the plate heat exchanger having the plurality ofrefrigerant channels is used for the evaporator, the liquid refrigerantcan be evenly distributed among the plurality of refrigerant channelswithout using a distributor. As a result, a uniform liquid refrigerantdistribution can be formed in the individual refrigerant channels toincrease the effective heat transfer area, thus improving heat exchangeperformance (cooling performance). This simplifies the structure of theplate heat exchanger without the need for a refrigerant distributor andalso reduces the size of the plate heat exchanger and improves theperformance of the plate heat exchanger.

In the refrigerator having the above structure, additionally, theevaporator may be constituted of a plurality of the plate heatexchangers connected in series as multiple stages.

In the above structure, because the plurality of plate heat exchangersare connected in series as multiple stages, the amount of heat exchangedby the evaporator (cooling capacity) can be increased. This improves thecooling performance.

In the refrigerator having the above structure, additionally, therefrigerant precoolers constituted of the vapor-liquid separators may bearranged in series as multiple stages at individual entrances of theplurality of plate heat exchangers.

In the above structure, because the refrigerant precoolers constitutedof the vapor-liquid separators are arranged in series as multiple stagesat the individual entrances of the plurality of plate heat exchangersconnected in series as multiple stages, only a liquid-phase refrigerantcan be supplied from the refrigerant precoolers to the respective plateheat exchangers. This allows the liquid refrigerant to be evenlydistributed among the individual refrigerant channels of the pluralityof plate heat exchangers to improve the heat exchange performance(cooling performance) and also reduces the size of the plate heatexchangers to a compact size.

In addition, a second aspect of the refrigerator according to thepresent invention is a refrigerator having a heat pump cycle formed bysequentially connecting a compressor that compresses a refrigerant, aswitching valve that switches a refrigerant cycle, a heat-source-sideheat exchanger, an expansion valve that adiabatically expands therefrigerant, and a utilization-side heat exchanger. An economizerthrough which a high-pressure liquid refrigerant always flows in onedirection via a refrigerant-flow-direction switching valve, whichevaporates some of the high-pressure liquid refrigerant to supercool therefrigerant, and which has a circuit for injecting the evaporatedmedium-pressure refrigerant into an intermediate inlet of the compressoris disposed between the heat-source-side heat exchanger and theutilization-side heat exchanger, and a refrigerant precooler thatprecools the refrigerant supplied to the utilization-side heat exchangeror the heat-source-side heat exchanger functioning as an evaporator isdisposed downstream of the economizer.

According to the second aspect, in switching between cooling andheating, the liquid refrigerant supercooled by the economizer can besupplied via the refrigerant-flow-direction switching valve to theutilization-side heat exchanger functioning as an evaporator in coolingor to the heat-source-side heat exchanger functioning as an evaporatorin heating, and the medium-pressure refrigerant evaporated by theeconomizer can be injected into the intermediate inlet of thecompressor. This improves the cooling/heating capacity and COP(coefficient of performance). At the same time, because the refrigerantprecooler disposed downstream of the economizer precools the refrigerantsupplied to the utilization-side heat exchanger or the heat-source-sideheat exchanger functioning as an evaporator in cooling or heating sothat the refrigerant can be supplied in a liquid phase with a dryness ofnearly zero, the temperature of the liquid refrigerant can be decreasedat the same pressure to achieve a larger temperature difference betweenthe liquid refrigerant and a heat exchange medium subjected to heatexchange on the evaporator side. This allows a larger amount of heat tobe exchanged at the same heat transfer coefficient, thus improving theheat exchange performance or reducing the size of the heat exchangersthemselves.

In one of the above aspects, additionally, the refrigerant precooler maydecrease the dryness of the refrigerant to nearly zero at an entrance ofthe evaporator.

According to the above aspect, because the refrigerant precoolerdecreases the dryness of the refrigerant to nearly zero at the entranceof the evaporator, only a single-phase liquid refrigerant can bereliably supplied to the evaporator. As a result, the temperature of theliquid refrigerant can be decreased at the same pressure to achieve alarger temperature difference between the liquid refrigerant and thecooled medium cooled by the evaporator. This allows a larger amount ofheat to be exchanged at the same heat transfer coefficient, thusimproving the cooling performance or reducing the size of theevaporator.

In one of the above aspects, additionally, the refrigerator may be aturbo refrigerator using a turbo compressor as the compressor.

According to the above aspect, it is possible to improve the performanceof a turbo refrigerator that has high-efficiency, high-performancecharacteristics and to reduce the size thereof.

According to the present invention, because the refrigerant supplied tothe evaporator can be precooled to a dryness of nearly zero and besupplied in a liquid phase to the evaporator, the temperature of theliquid refrigerant can be decreased at the same pressure to achieve alarger temperature difference between the liquid refrigerant and thecooled medium cooled by the evaporator. This ensures the economizereffect and allows a larger amount of heat to be exchanged at the sameheat transfer coefficient, thus improving the cooling performance orreducing the size of the evaporator.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a refrigeration cycle diagram of a turbo refrigeratoraccording to a first embodiment of the present invention.

FIG. 2 is a P-h graph of the turbo refrigerator shown in FIG. 1.

FIG. 3 is a graph showing the relationship between the refrigerantdryness and the overall heat transfer U of the turbo refrigerator shownin FIG. 1.

FIG. 4 is a refrigeration cycle diagram of a turbo refrigeratoraccording to a second embodiment of the present invention.

FIG. 5 is a refrigeration cycle diagram of a turbo refrigeratoraccording to a third embodiment of the present invention.

FIG. 6 is a refrigeration cycle diagram of a turbo refrigeratoraccording to a fourth embodiment of the present invention.

EXPLANATION OF REFERENCE SIGNS

1: turbo refrigerator

2: two-stage turbo compressor

3: condenser

3A: heat-source-side air heat exchanger

4: economizer

4A: intermediate heat exchanger (intermediate cooler)

5: main expansion valve

6A, 6B: plate heat exchanger

7: evaporator

7A: utilization-side heat exchanger

8, 8A: refrigeration cycle (heat pump cycle)

15, 25, 35, 36: refrigerant precooler

15A: refrigerant-refrigerant heat exchanger

16: refrigerant-precooling expansion valve

17, 26, 37, 39: gas circuit

20A, 20B: four-way switching valve

25A, 35A, 36A: vapor-liquid separator

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below withreference to the drawings.

First Embodiment

A first embodiment of the present invention will be described belowusing FIGS. 1 to 3.

FIG. 1 shows a refrigeration cycle diagram of a turbo refrigeratoraccording to the first embodiment of the present invention. A turborefrigerator 1 has a refrigeration cycle 8 formed as a closed circuit bysequentially connecting a two-stage turbo compressor 2, a condenser 3,an economizer 4, a main expansion valve 5, and an evaporator 7 includingtwo plate heat exchangers 6A and 6B connected in series as multiplestages.

The two-stage turbo compressor 2, a multistage compressor driven by aninverter motor 9, has an intermediate inlet 2C disposed between firstand second impellers (not shown) in addition to an inlet 2A and anoutlet 2B and is configured to sequentially compress a low-pressurerefrigerant gas taken in from the inlet 2A by centrifugation throughrotation of the first and second impellers and to discharge thecompressed high-pressure refrigerant gas from the outlet 2B. Thecondenser 3 condenses the high-pressure refrigerant gas supplied fromthe two-stage turbo compressor 2 by heat exchange with cooling watercirculated via a cooling-water circuit 10.

The economizer 4 is constituted of an intermediate cooler 4A formed of arefrigerant-refrigerant heat exchanger, such as a double-pipe heatexchanger, that performs heat exchange between the liquid refrigerantflowing through the main circuit of the refrigeration cycle 8 and arefrigerant shunted from the main circuit and depressurized by aneconomizer expansion valve 11 to supercool the liquid refrigerantflowing through the main circuit by means of the latent heat ofevaporation of the refrigerant. In addition, the intermediate cooler 4Ahas a gas circuit 12 for injecting the refrigerant gas evaporated whensupercooling the liquid refrigerant through the intermediate inlet 2C ofthe two-stage turbo compressor 2 into a medium-pressure compressedrefrigerant, thus constituting an intermediate-cooler economizer cycle.

The main expansion valve 5 adiabatically expands the refrigerantsupercooled through the economizer 4 and supplies it to the evaporator7. The evaporator 7 is constituted of the plate heat exchangers 6A and6B connected in series as multiple stages, each constituted of aplurality of plates stacked in parallel such that a plurality ofrefrigerant channels and a plurality of cooled-medium channels (coldwater channels) are alternately arranged, and the evaporator 7evaporates the refrigerant by heat exchange with cold water circulatedthrough the cooled-medium channels (cold water channels) via acold-water circuit 13 to cool the cold water to a preset temperature,for example, 7° C., by means of the latent heat of evaporation thereof.The refrigerant and the cold water preferably flow in counterflow.

In addition to the above structure, in this embodiment, a refrigerantprecooler 15 is further disposed downstream of the economizer 4 toprecool the refrigerant supplied to the evaporator 7 to a dryness ofnearly zero. This refrigerant precooler 15 is constituted of arefrigerant-refrigerant heat exchanger 15A, such as a double-pipe heatexchanger, having nearly the same structure as the above intermediatecooler 4A for the economizer 4 and performs heat exchange between theliquid refrigerant flowing through the main circuit of the refrigerationcycle 8 and a refrigerant shunted from the main circuit downstream ofthe economizer 4 and depressurized by a refrigerant-precooling expansionvalve 16 to cool the liquid refrigerant flowing through the main circuitby means of the latent heat of evaporation of the refrigerant. Inaddition, the refrigerant precooler 15 has a gas circuit 17 forreturning the refrigerant gas evaporated when cooling the liquidrefrigerant to a refrigerant intake circuit between the evaporator 7 andthe two-stage turbo compressor 2.

Next, the operation of this embodiment will be described with referenceto a P-h graph shown in FIG. 2.

A low-temperature, low-pressure refrigerant gas A taken in from theinlet 2A of the two-stage turbo compressor 2 is compressed from point Ato point B by the first impeller, is mixed with the medium-pressurerefrigerant gas injected from the intermediate inlet 2C to reach pointC, and is taken in through and compressed to point D by the secondimpeller. The refrigerant discharged in this state from the two-stageturbo compressor 2 is cooled and condensed into a high-pressure liquidrefrigerant at point E by the condenser 3. Some of the liquidrefrigerant at point E is shunted and depressurized to point F by theeconomizer expansion valve 11 to flow into the intermediate cooler 4A.This medium-pressure refrigerant is subjected, in the intermediatecooler 4A, to heat exchange with the liquid refrigerant E flowingthrough the main circuit of the refrigeration cycle 8 to absorb heatfrom the liquid refrigerant E, thus evaporating, and is then injectedvia the gas circuit 12 through the intermediate inlet 2C of thetwo-stage turbo compressor 2 into the medium-pressure refrigerant gasbeing compressed.

On the other hand, the liquid refrigerant E in the main circuitsubjected to heat exchange with the refrigerant at point F in theintermediate cooler 4A for the economizer 4 is supercooled to point Gand reaches the refrigerant precooler 15. Some of the liquid refrigerantexiting the intermediate cooler 4A is shunted and depressurized to pointH by the refrigerant-precooling expansion valve 16 to flow into therefrigerant precooler 15 for heat exchange with the liquid refrigerant Gin the main circuit. This refrigerant at point H is subjected, in therefrigerant precooler 15, to heat exchange with the liquid refrigerant Gin the main circuit, thus evaporating, and is then returned via the gascircuit 17 to the refrigerant intake circuit between the evaporator 7and the two-stage turbo compressor 2 to meet the refrigerant A exitingthe evaporator 7 through point I.

The liquid refrigerant at point G is cooled to point J by precooling inthe refrigerant precooler 15, is depressurized to point K by the mainexpansion valve 5, and reaches the entrance of the evaporator 7. Thelow-pressure refrigerant at point K, as shown in FIG. 2, is asingle-phase liquid refrigerant with a dryness of nearly zero. Thus, therefrigerant precooler 15 disposed between the economizer 4 and theevaporator 7 can further precool the refrigerant supercooled by theeconomizer 4 to supply a single-phase liquid refrigerant with a drynessof nearly zero to the evaporator 7.

The refrigerant supplied to the evaporator 7 in a single liquid phase isfirst evenly distributed among the plurality of refrigerant channels ofthe front-end plate heat exchanger 6A and flows therethrough while beingsubjected to heat exchange with the cold water circulated through thecooled-medium channels (cold water channels) via the cold-water circuit13 so that some refrigerant evaporates. The refrigerant flowing out ofthe front-end plate heat exchanger 6A then flows into the back-end plateheat exchanger 6B and is similarly subjected to heat exchange with thecold water so that the remaining refrigerant evaporates. Thus, the coldwater circulated via the cold-water circuit 13 is cooled to a presettemperature and is supplied to the load side. The refrigerant flowingthrough the plate heat exchangers 6A and 6B, which turns into a slightlysuperheated low-pressure gas refrigerant A at the exit thereof, meetsthe gas refrigerant from the gas circuit 17 and is taken into thetwo-stage turbo compressor 2 again, with the subsequent operation beingthe same as above.

Thus, this embodiment provides the following advantages.

Because the refrigerant can be supplied to the evaporator 7 in a singleliquid phase with a dryness of nearly zero, the temperature of theliquid refrigerant can be decreased at the same pressure to achieve alarger temperature difference between the liquid refrigerant and thecooled medium (cold water) cooled by the evaporator 7. This ensuresimprovement in the refrigeration capacity and COP (coefficient ofperformance) by the economizer 4 and allows a larger amount of heat tobe exchanged at the same heat transfer coefficient, thus improving thecooling performance or reducing the size of the evaporator 7.

Specifically, as shown in FIG. 3, the refrigerant supplied to theevaporator 7 (plate heat exchanger 6A) is normally in a vapor-liquidtwo-phase state and has a dryness of about 0.1 and an overall heattransfer U of A1 at the entrance thereof and an overall heat transfer Uof B1 at the exit thereof. As in Patent Document 2 above, therefore, avapor-liquid separator can be disposed between the front-end plate heatexchanger 6A and the back-end plate heat exchanger 6B to separate thevapor-phase refrigerant at the exit of the front-end plate heatexchanger 6A, thereby improving the overall heat transfer U at the exitto B2. Because the amount of heat Q exchanged by the evaporator 7 isrepresented by Q=A*U*ΔTm, where A is the heat transfer area and ΔTm isthe volume-change temperature difference, the heat transfer area A canbe reduced to reduce the size of the evaporator 7 if the overall heattransfer U is increased to increase the amount of heat Q exchanged. Asin this embodiment, if the refrigerant precooler 15 is provided toprecool the refrigerant supplied to the evaporator 7 so that therefrigerant dryness at the evaporator entrance is decreased to nearlyzero and accordingly the overall heat transfer U is increased to A2, itis possible to improve the cooling performance or to reduce the size ofthe evaporator 7 more effectively than in the case of the refrigeratordisclosed in Patent Document 2.

In addition, because the refrigerant precooler 15 uses some of theliquid refrigerant circulated through the refrigeration cycle 8 as aheat sink to precool the liquid refrigerant by means of the latent heatof evaporation thereof, it is possible to efficiently precool the liquidrefrigerant and also to simplify the structure of the refrigerantprecooler 15 for ease of installation without the need to supply anexternal heat sink.

In addition, because the refrigerant precooler 15 is constituted of therefrigerant-refrigerant heat exchanger 15A, such as a double-pipe heatexchanger, that performs refrigerant-refrigerant heat exchange and thathas the gas circuit 17 for returning the evaporated refrigerant to therefrigerant intake circuit between the evaporator 7 and the two-stageturbo compressor 2, the refrigerant precooler 15 needs no specialstructure, and an existing refrigerant-refrigerant heat exchanger can bedirectly applied. Accordingly, the refrigerant precooler 15 can beprovided at low cost.

In addition, because the economizer 4 and the refrigerant precooler 15are constituted of refrigerant-refrigerant heat exchangers, such asdouble-pipe heat exchangers, that perform refrigerant-refrigerant heatexchange, the economizer 4 and the refrigerant precooler 15 do notchange the composition of the refrigerant even if the refrigerationcycle 8 uses a mixed refrigerant, such as R410A, whose compositionchanges as a result of self-expansion, so that the rated capacity can bedelivered without the possibility of unstable capacity due to changes inthe composition of the refrigerant.

In addition, because the refrigerant precooler 15 can precool therefrigerant to a dryness of nearly zero and supply it to the evaporator7 in a single liquid phase, even if the plate heat exchangers 6A and 6Bhaving the plurality of refrigerant channels are used for the evaporator7, the liquid refrigerant can be evenly distributed among the pluralityof refrigerant channels without using a distributor. This allowsformation of a uniform liquid refrigerant distribution in the individualrefrigerant channels to increase the effective heat transfer area, thusimproving the heat exchange performance (cooling performance), and alsosimplifies the structure of the plate heat exchangers 6A and 6B. Inparticular, the heat exchange efficiency can be increased because anorifice mechanism can be omitted for reduced pressure loss. In addition,because the evaporator 7 can be constituted by connecting the pluralityof plate heat exchangers 6A and 6B in series as multiple stages, theamount of heat exchanged by the evaporator 7 can be increased to improvethe cooling performance.

In addition, because the superheated refrigerant gas evaporated by therefrigerant precooler 15 is returned to the refrigerant intake circuitbetween the evaporator 7 and the two-stage turbo compressor 2 via thegas circuit 17, even if some refrigerant droplets are carried over fromthe evaporator 7, they can be reliably evaporated. Thus, carry-over ofrefrigerant droplets to the two-stage turbo compressor 2 can beprevented.

In this embodiment, the circuit for supplying some of the liquidrefrigerant to the refrigerant precooler 15 may be constituted of acircuit branched from the circuit for shunting some of the liquidrefrigerant from the upstream side of the economizer 4 to theintermediate cooler 4A, as indicated by the broken line in FIG. 1.

Second Embodiment

Next, a second embodiment of the present invention will be describedusing FIG. 4.

This embodiment differs from the first embodiment described above in thestructure of a refrigerant precooler 25. The other points are similar tothose of the first embodiment, and a description thereof will thereforebe omitted.

In this embodiment, the refrigerant precooler 25 is constituted of avapor-liquid separator 25A disposed on the entrance side of theevaporator 7 (plate heat exchanger 6A). A vapor-phase refrigerantseparated by the vapor-liquid separator 25A is returned to therefrigerant intake circuit between the evaporator 7 and the two-stageturbo compressor 2 via a gas circuit 26 having an on/off valve 27.

As described above, because the refrigerant precooler 25 constituted ofthe vapor-liquid separator 25A disposed on the entrance side of theevaporator 7 (plate heat exchanger 6A) can supply a single liquid phasewith a dryness of nearly zero to the evaporator 7 (plate heat exchanger6A), the same effects and advantages as the first embodiment describedabove can be provided. In addition, the vapor-liquid separator 25A needsno special structure, and existing vapor-liquid separators widely usedfor refrigerators can be directly applied, so that the refrigerantprecooler 25 can be provided at low cost.

This embodiment illustrates the case where the single plate heatexchanger 6A is provided as the evaporator 7; naturally, a plurality ofplate heat exchangers may be connected in series in multiple stages, asin the first embodiment.

Third Embodiment

Next, a third embodiment of the present invention will be describedusing FIG. 5.

This embodiment differs from the first embodiment described above in thestructure of refrigerant precoolers 35 and 36. The other points aresimilar to those of the first embodiment, and a description thereof willtherefore be omitted.

In this embodiment, the evaporator 7 constituted of the plurality ofplate heat exchangers 6A and 6B connected in series as multiple stagesis provided with refrigerant precoolers 35 and 36 constituted ofvapor-liquid separators 35A and 36A, respectively, arranged in series asmultiple stages at the entrances of the respective plate heat exchangers6A and 6B. In addition, vapor-phase refrigerants separated by thevapor-liquid separators 35A and 36A are returned to the refrigerantintake circuit between the evaporator 7 and the two-stage turbocompressor 2 via gas circuits 37 and 39 having on/off valves 38 and 40,respectively.

As described above, if the evaporator 7 is constituted of the pluralityof plate heat exchangers 6A and 6B connected in series as multiplestages, the refrigerant precoolers 35 and 36 constituted of thevapor-liquid separators 35A and 36A can be arranged in series asmultiple stages at the entrances of the respective plate heat exchangers6A and 6B to supply only a single-phase liquid refrigerant with adryness of nearly zero from the refrigerant precoolers 35 and 36 to therespective plate heat exchangers 6A and 6B. Thus, the same effects andadvantages as the first embodiment described above can be provided. Inaddition, because the liquid refrigerant can be evenly distributed amongthe individual refrigerant channels of the plurality of plate heatexchangers 6A and 6B, it is possible to improve the heat exchangeperformance (cooling performance) and to reduce the size of the plateheat exchangers 6A and 6B to a compact size.

Fourth Embodiment

Next, a fourth embodiment of the present invention will be describedusing FIG. 6.

This embodiment differs from the first embodiment described above inthat a four-way switching valve 20A for switching the refrigerationcycle and a four-way switching valve 20B for switching the refrigerantflow direction are provided to form a heat pump cycle so that the turborefrigerator 1 can perform heating and cooling. The other points aresimilar to those of the first embodiment, and a description thereof willtherefore be omitted.

The turbo refrigerator 1 of this embodiment includes the four-wayswitching valve 20A capable of reversing the refrigeration cycle betweenthe discharge pipe and the intake pipe of the two-stage turbo compressor2 to form a heat pump cycle 8A that can be switched between a coolingcycle and a heating cycle and also includes, instead of the water-cooledcondenser 3, an air heat exchanger 3A equipped with a fin-and-tuberefrigerant distributor 21 and capable of using air 10A as a heatsource.

In addition, the four-way switching valve 20B capable of switching therefrigerant flow direction is disposed between the heat-source-side airheat exchanger 3A and a utilization-side heat exchanger 7A constitutedof the plate heat exchangers 6A and 6B connected in series as multiplestages so that a high-pressure liquid refrigerant always flows in onedirection through the economizer 4 and the refrigerant precooler 15 toachieve an economizer effect and a refrigerant-precooling effect ineither of cooling and heating.

In the above structure, the four-way switching valves 20A and 20B can beswitched to the direction indicated by the solid arrows so that theheat-source-side air heat exchanger 3A functions as a condenser and theutilization-side heat exchanger 7A functions as an evaporator, therebysupplying cold water from the utilization-side heat exchanger 7A toachieve cooling. On the other hand, the four-way switching valves 20Aand 20B can be switched to the direction indicated by the dashed arrowsso that the utilization-side heat exchanger 7A functions as a condenserand the heat-source-side air heat exchanger 3A functions as anevaporator, thereby supplying hot water from the utilization-side heatexchanger 7A to achieve heating. During the operation, the refrigerantflows in one direction through the economizer 4 and the refrigerantprecooler 15 to provide an economizer effect and arefrigerant-precooling effect in either of cooling and heating, as inthe above embodiments.

According to this embodiment, therefore, the liquid refrigerantsupercooled by the economizer 4 can be supplied to the heat exchangerfunctioning as an evaporator in either of cooling and heating (theutilization-side heat exchanger 7A in cooling and the heat-source-sideair heat exchanger 3A in heating), and the medium-pressure refrigerantevaporated by the economizer 4 can be injected into the intermediateinlet 2C of the two-stage turbo compressor 2. This improves thecooling/heating capacity and COP (coefficient of performance).

At the same time, because the refrigerant precooler 15 disposeddownstream of the economizer 4 precools the refrigerant supplied to theutilization-side heat exchanger 7A or the heat-source-side air heatexchanger 3A functioning as an evaporator in cooling or heating so thatthe refrigerant can be supplied in a single liquid phase with a drynessof nearly zero, the temperature of the liquid refrigerant can bedecreased at the same pressure to achieve a larger temperaturedifference between the liquid refrigerant and the heat exchange mediumsubjected to heat exchange on the evaporator side. This allows a largeramount of heat to be exchanged at the same heat transfer coefficient,thus improving the heat exchange performance or reducing the size of theheat exchangers themselves.

In this embodiment, the switching valves 20A and 20B for switching therefrigeration cycle and the refrigerant flow direction do notnecessarily have to be four-way switching valves; for example, they canbe replaced with bridge circuits composed of four electromagnetic on/offvalves. In addition, the refrigerant precooler 15 can be constituted ofthe vapor-liquid separator 25A or 35A and 36A as in the second and thirdembodiments shown in FIGS. 4 and 5.

In addition, the present invention is not limited to the inventionaccording to the above embodiments; modifications are permitted whereappropriate without departing from the spirit thereof. Naturally, thepresent invention can be similarly applied to, for example, amultistage-economizer turbo refrigerator constituted of a multistageturbo compressor including three or more stages. In addition, althoughan intermediate-cooler economizer cycle has been described as an exampleof an economizer cycle, the present invention can be similarly appliedto a vapor-liquid-separator economizer cycle using a vapor-liquidseparator. In addition, the evaporator used is not limited to a plateheat exchanger; naturally, another type of evaporator, such as ashell-and-tube heat exchanger or a fin-and-tube heat exchanger, can beused instead.

1. A refrigerator having a refrigeration cycle formed by sequentiallyconnecting a compressor that compresses a refrigerant, a condenser thatcondenses the high-pressure gas refrigerant, an economizer thatevaporates some of the condensed liquid refrigerant to cool the liquidrefrigerant by means of the latent heat of evaporation thereof and thathas a circuit for injecting the evaporated medium-pressure refrigerantinto an intermediate inlet of the compressor, an expansion valve thatadiabatically expands the liquid refrigerant, and an evaporator thatevaporates the adiabatically expanded refrigerant, wherein a refrigerantprecooler that precools the refrigerant supplied to the evaporator isdisposed between the economizer and the evaporator.
 2. The refrigeratoraccording to claim 1, wherein the refrigerant precooler evaporates someof the liquid refrigerant to cool the liquid refrigerant by means of thelatent heat of evaporation thereof and has a circuit for returning theevaporated refrigerant to a refrigerant intake circuit between theevaporator and the compressor.
 3. The refrigerator according to claim 1,wherein the refrigerant precooler is constituted of arefrigerant-refrigerant heat exchanger that precools the liquidrefrigerant by heat exchange with a refrigerant shunted from the liquidrefrigerant and depressurized and that has a circuit for returning theevaporated refrigerant to a refrigerant intake circuit between theevaporator and the compressor.
 4. The refrigerator according to claim 3,wherein the economizer is constituted of an intermediate cooler thatevaporates some of the condensed liquid refrigerant to cool the liquidrefrigerant by means of the latent heat of evaporation thereof, and therefrigerant is a mixed refrigerant such as R410A.
 5. The refrigeratoraccording to claim 1, wherein the refrigerant precooler is constitutedof a vapor-liquid separator that separates the liquid refrigerant into aliquid-phase refrigerant and a vapor-phase refrigerant and that has acircuit for returning the vapor-phase refrigerant having precooled theliquid-phase refrigerant by evaporation and separation to a refrigerantintake circuit between the evaporator and the compressor.
 6. Therefrigerator according to claim 1, wherein the evaporator is constitutedof a plate heat exchanger including a plurality of plates stacked inparallel such that a plurality of refrigerant channels and a pluralityof cooled-medium channels are alternately arranged.
 7. The refrigeratoraccording to claim 6, wherein the evaporator is constituted of aplurality of the plate heat exchangers connected in series as multiplestages.
 8. The refrigerator according to claim 7, wherein therefrigerant precoolers constituted of the vapor-liquid separators arearranged in series as multiple stages at individual entrances of theplurality of plate heat exchangers.
 9. A refrigerator having a heat pumpcycle formed by sequentially connecting a compressor that compresses arefrigerant, a switching valve that switches a refrigerant cycle, aheat-source-side heat exchanger, an expansion valve that adiabaticallyexpands the refrigerant, and a utilization-side heat exchanger, whereinan economizer through which a high-pressure liquid refrigerant alwaysflows in one direction via a refrigerant-flow-direction switching valve,which evaporates some of the high-pressure liquid refrigerant tosupercool the refrigerant, and which has a circuit for injecting theevaporated medium-pressure refrigerant into an intermediate inlet of thecompressor is disposed between the heat-source-side heat exchanger andthe utilization-side heat exchanger, and a refrigerant precooler thatprecools the refrigerant supplied to the utilization-side heat exchangeror the heat-source-side heat exchanger functioning as an evaporator isdisposed downstream of the economizer.
 10. The refrigerator according toclaim 1, wherein the refrigerant precooler decreases the dryness of therefrigerant to nearly zero at an entrance of the evaporator.
 11. Therefrigerator according to claim 10, wherein the refrigerator is a turborefrigerator using a turbo compressor as the compressor.